Diode laser configurations with vertical laser diode stacks (vertical stacks) of laser diode bars, which are actively cooled with microchannel heat sinks, can serve as pumplight sources for diode-pumped high-performance solid state lasers. With a sufficiently large stack height (e.g., approximately 50 laser diode bars), these stacks have an approximately identically sized beam parameter product in a horizontal direction (i.e., along the slow axis (“SA”)) and in a vertical direction (i.e., along the fast axis (“FA”)). This facilitates coupling of the radiation emitted by these vertical stacks into a nearly rotationally-symmetrical light mixer thereby approximately maintaining the brilliance of the pump radiation. The pump radiation is homogenized in the light mixer through multiple reflection. The radiation emitted from the light mixer is suited to reproduce a round pump spot on a laser crystal. The service life of the actively cooled vertical stacks is limited to only about 10,000 hours.
German patent application, serial number DE 100 61 265 A1, discloses quasi-passively cooled diode laser configurations with horizontal laser diode stacks (i.e., a 2D passive stack, or a horizontal stack, respectively) as pump light source for high-performance solid state lasers. In these diode laser configurations, the individual diode bars are disposed such that they are not on top of each other in the FA direction, but next to each other in the SA direction. Additionally, the individual diode bars can be slightly offset in steps in the FA direction. The horizontal stacks are more reliable than vertical stacks, since the electric function is separate from cooling and also due to the larger cooling structures and the greatly reduced number of sealing elements.
The optical format of the laser beam produced by the laser diode bars disposed next to each other in the SA direction is disadvantageous. In contrast to a vertical stack, the asymmetry of the beam quality of the horizontal stack is further increased along the SA direction by the arrangement of the bars next to each other and by the resulting widening of the overall cross-section of the emitted radiation. Moreover, the relatively large height of the horizontal stacks in the FA direction requires FA collimator lenses with an unusually large focus length for optically aligned stacking in the FA direction. The small divergence of the beams collimated in this manner requires very high precision of the optical components in the further optical path. The overall height of the number of stacked horizontal stacks required for a symmetrical beam quality is moreover too large for practical applications. For this reason, a beam shaping optics is required to obtain approximate symmetry of the output radiation of horizontal stacks.
German patent application, serial number DE 199 39 750 A1, discloses a beam shaping optics for combining three laser beams provided by three diode bars that are disposed in one common horizontal plane, into one superposed laser beam. This optical arrangement reduces the extension of the laser radiation in the SA direction. A correcting optics is disposed in the optical path directly after the diode bars for beam collimation in the FA direction and also in the SA direction. The optical arrangement includes lateral displacement elements for lateral displacement (i.e., parallel displacement) of the two outer laser beams along the SA direction, which include a beam deflecting element and a coupling element (e.g., a prismatic cube).
The German patent application, serial number DE 199 39 750 A1, moreover discloses a beam shaping optics for combining two laser beams provided by diode bars that are disposed next to each other in the SA direction and are offset from each other in small steps in the FA direction, into a combined laser beam. This optical arrangement has two plane-parallel plates disposed on top of each other in the FA direction and at an angle to the incoming radiation in the SA direction, and through which the radiation is transmitted. The refraction of light on the entering and exiting surfaces, which are disposed at an angle to the beam propagation direction, offsets the two incoming laser beams laterally in the SA direction by half the center-to-center distance of the beams each, thereby shifting them on top of each other like a comb (so-called interleaving).